Radiopaque markers and medical devices comprising binary alloys of titanium

ABSTRACT

There is disclosed medical devices, such as stents, guidewires and embolic filters, comprising a binary alloy of titanium and one binary element selected from platinum, palladium, rhodium, and gold. There is also disclosed a radiopaque marker comprising the disclosed binary alloy, as well as medical devices having the radiopaque marker attached thereto. Methods of attaching the radiopaque marker to the medical devices, such as by welding, are also disclosure also disclosed.

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/748,797, filed on May 15, 2007, the contents of which areincorporated herein by reference.

The present disclosure relates to binary alloys of titanium that can beused as alternatives to linear elastic nitinol alloys. The presentdisclosure also relates to any product or medical device comprising suchalloys, including those in which a material having a high elastic limitis desired. In addition, because of the high radiopaque propertiesassociated with such alloys, the present invention also relates toradiopaque markers and medical devices, such as stents, guidewires,embolic protection devices, or other components of a stent deliverysystem, comprising such alloys. The present disclosure also relates tomedical devices having the radiopaque markers attached thereto.

Stents are generally thin walled tubular-shaped devices composed ofcomplex patterns of interconnecting struts which function to hold open asegment of a blood vessel or other body lumen such as a coronary artery.They also are suitable for supporting a dissected arterial lining orintimal flap that can occlude a vessel lumen.

Guidewires are used for advancing intraluminal devices to the desiredlocation within a body lumen in angioplasty, stent delivery, atherectomyand other vascular procedures. A conventional guidewire usuallycomprises an elongated core member with one or more tapered sectionsnear the distal end thereof and a flexible body such as a helical coilor a tubular body of polymeric material disposed about the distalportion of the core member. The flexible body may extend proximally toan intermediate portion of the guidewire.

Embolic protection devices serve to capture and remove the debriscreated by angioplasty, stent delivery, atherectomy and other vascularprocedures. It prevents the debris from flowing downstream and blockingthe artery. One type of embolic protection device is filter-based, whichallows the blood in the artery to continue flowing while the filtertraps the debris.

Traditional stent delivery systems comprise a guidewire, astent-delivery catheter, a stent, and may include an embolic protectiondevice. A stent is typically implanted using a catheter which isinserted at an easily accessible location and then advanced through thevasculature to the deployment site. The stent is initially maintained ina radially compressed or collapsed state to enable it to be maneuveredthrough the lumen. Once in position, the stent is deployed. In the caseof self-expanding stents, deployment is achieved by the removal of arestraint, such as the retraction of a delivery sheath. In the case ofballoon expandable stents, deployment is achieved by inflation of adilatation balloon about which the stent is carried on a stent-deliverycatheter.

Stents, guidewires, embolic protection devices, and other components ina stent delivery system can be constructed at least partially using asuperelastic material, such as nickel-titanium alloys, also known asnitinol. An embolic filter made of nitinol is shown in, for example,U.S. Pat. No. 6,179,859 (Bates et al.), which is herein incorporated byreference. A guidewire made from nitinol is shown in, for example, U.S.Pat. No. 5,341,818 (Abrams), which is herein incorporated by reference.

In general, superelasticity implies that the material can undergo alarge degree of reversible strain as compared to common steel. In atechnical sense, the term “superelasticity” and sometimes“pseudoelasticity” refer to an isothermal transformation in nitinol.More specifically, it refers to stress inducing a martensitic phase froman austenitic phase at a temperature above the martensitictransformation temperature.

Nitinol alloys, for example, exhibit both superelasticity and the shapememory effect. The literature describes various processing techniques toenhance these valuable properties. These techniques include changing therelative amounts of nickel and titanium, alloying the nickel-titaniumwith other elements, heat treating the alloy, and mechanical processingof the alloy. Examples of such techniques include U.S. Pat. No.4,310,354 (Fountain), which discloses processes for producing a shapememory nitinol alloy having a desired transition temperature; U.S. Pat.No. 6,106,642 (DiCarlo), which discloses a process for improvingductility of nitinol; U.S. Pat. No. 5,843,244 (Pelton), which disclosescold working and annealing a nitinol alloy to lower a transformationtemperature; U.S. Publication No. US 2003/0120181A1, published Jun. 26,2003, which discloses work-hardened pseudoelastic guide wires; U.S. Pat.No. 4,881,981 (Thoma et al.), which discloses a process for adjustingthe physical and mechanical properties of a shape memory alloy member byincreasing the internal stress level of the alloy by cold work and heattreatment; and U.S. Pat. No. 6,706,053 (Boylan et al.) which teachesadding a ternary element to a nickel-titanium alloy to enhanceengineering properties suitable for an embolic filter.

Superelastic characteristics generally allow the metal stent to bedeformed by collapsing the stent and creating stress which causes thesuperelastic material to reversibly change to the martensitic phase.Once the stress is released, the martensitic phase reverses back toaustenitic phase. This release of stress such that the stent returnstowards its original undeformed shape through isothermal transformationback to the austenitic phase is described as “self-expanding.”

Superelastic nitinol alloys exhibit very high reversible strain,typically around 7-10%. On a stress-strain plot of a superelastic alloy,stress stays relatively constant over a large range of strain. Thisbehavior results in a plateau in the otherwise relatively linearstress-strain relationship. For certain nitinol alloys, however, thestrain range where stress stays constant over is very short ornon-existent. As a result, the stress and strain of the alloys exhibitsa linear relationship without a plateau. Such nitinol alloys arereferred to as linear elastic nitinol. Linear elastic nitinol stillexhibits significant reversible strain (ca. 2-3%) and have shape memorycharacteristics.

The stress plateau in superelastic alloys is desirable when, forinstance, it is desirable to minimize the amount of force exerted by aself-expanding stent against a vessel wall as it expands radiallyoutward. In other instances, the stress plateau is less desirable. Forexample, it may be preferable to have a guidewire's distal core made oflinear elastic nitinol so that the guidewire provides bend support to anoverlying balloon catheter. A guidewire with a linear elastic core mayalso transmit a higher torsional load along its length in comparisonwith a guidewire having a superelastic alloy distal core.

When selecting a material for making a medical device, severalproperties are considered, First, yield stress (YS) is the stress valueat which the relationship between the stress and strain are no longerlinear and permanent deformation occurs. Elastic modulus (E) is therelationship between the applied stress and a material's exhibitedstrain, and is expressed as the slope of the initial, linear portion ofa stress-strain plot. Elastic strain limit is the amount of strain thata material can withstand without exhibiting permanent deformation uponunloading. In this disclosure, a material's elastic strain limit isdefined as its yield stress divided by its elastic modulus (YS/E).Consequently, a material's elastic strain limit can be increased byraising its yield stress and/or reducing its elastic modulus. Formetallic materials, elastic modulus is generally an invariant property,which is not significantly influenced by processing history, while yieldstress is very dependent on the prior thermal-mechanical processing ofthe material. Cold work is known to increase the yield stress of ametal.

Linear elastic nitinol alloys have inherently low elastic modulus whilein its martensitic phase (ca. 8 Msi in comparison with ca. 30 Msi for304 stainless steel). However, martensitic binary nitinol in theannealed condition typically has a low yield stress. As a result, ittypically has a very low elastic strain limit and is not suitable formaking medical devices which require high elastic limit, such as adistal core or shaping ribbon for a guidewire, or a filter basket of anembolic protection device. Imparting an appropriate amount of cold workon the martensitic binary nitinol can increases its yield stress andelastic strain limit.

Self-expanding, nickel-titanium stents have long been useful andvaluable to the medical field. But a distinct disadvantage withself-expanding nickel-titanium stents is the fact that they are notsufficiently radiopaque.

An intracorporeal device and its delivery system should be radiopaque orfluoroscopically visible. For instance, accurate stent placementrequires real time visualization to allow the physician to track thedelivery catheter through the patient's vasculature and precisely placethe stent at the site of a lesion. This is typically accomplished byfluoroscopy or similar x-ray visualization procedures. For a device tobe fluoroscopically visible it must be more absorptive of x-rays thanthe surrounding tissue. Good radiopacity is therefore a useful featurefor self-expanding nickel-titanium stents to have.

Radiopacity can be improved by increasing the strut thickness of thenickel-titanium stent. But increasing strut thickness detrimentallyaffects the flexibility of the stent, which is a quality necessary forease of delivery. Another complication is that radiopacity and radialforce vary with strut thickness.

Radiopacity can also be improved through coating processes such assputtering, plating, or co-drawing gold or similar heavy metals onto thestent. These processes, however, create complications such as materialcompatibility, galvanic corrosion, high manufacturing cost, coatingadhesion or delamination, biocompatibility, loss of coating integrityfollowing collapse and deployment of the stent. Further, they may retardthe dimensional recovery of a self expanding stent during deployment andpotentially increase the delivery profile of the crimped stent.

In addition, radiopacity can be improved by alloy addition, such as byalloying nickel-titanium with a ternary element. This approach, however,typically requires one to strike a balance between achieving sufficientdegree of radiopacity and maintaining the desirable superelasticengineering properties typical of a binary nickel-titanium.

One method for increasing fluoroscopic visibility is the physicalattachment of radiopaque markers to the intracorporeal device and itsdelivery system. The attachment can be accomplished by varioustechniques, such as welding. It is well known, however, that nitinol canbe difficult to weld to another metal or alloy since the nickel ortitanium in nitinol will typically combine with one or more elements inthe other material to product intermetallic compounds. Theseintermetallic compounds usually cause cracking during cooling and havean adverse impact on weld joint ductility.

What is needed therefore is a radiopaque marker that is compatible withmaterials in the medical devices mentioned above and their deliverysystems. Such a marker should be sufficiently radiopaque to be readilyvisible using fluoroscopy procedures, and also can be readily attachedto the medical device and its delivery system.

Another approach is to make the medical devices using alloys other thannitinol that have a high elastic strain limit, in addition to beneficialradiopaque properties, which makes the devices themselves visible usingfluoroscopy procedures. The challenge is to identify or develop aradiopaque alloy with shape memory characteristics that can be used inplace of nitinol in medical devices.

SUMMARY OF THE INVENTION

The present disclosure is generally directed to binary alloys oftitanium and one binary element chosen from platinum, palladium,rhodium, and gold. In one embodiment, there is disclosed a radiopaquemarker comprising such alloys. The disclosure is also directed to amedical device, such as a stent, guidewire, or embolic filter device,having the radiopaque marker attached thereto. In one embodiment, theradiopaque marker is attached to the medical device by welding, such asfusion welding, wherein one or both components is melted.

Another aspect of the present disclosure is directed to a stent deliverysystem comprising an expandable or self-expanding section, and aradiopaque marker comprising a binary alloy of titanium and one elementchosen from platinum, palladium, rhodium, and gold integrally attachedto the expandable or self-expanding section.

There is also disclosed a method of fabricating a medical devicecomprising a radiopaque marker. In one embodiment, the method compriseswelding to an expandable or self-expanding section of a medical device,such as by fusion welding, a radiopaque marker described herein.

The present disclosure is also directed to medical devices having a highelastic limit or yield stress comprised of the binary alloys disclosedherein, as well as a high radiopacity are desirable. For example, in oneembodiment such medical devices comprises a binary alloy of titanium andone binary element chosen from platinum, palladium, and gold.Non-limiting examples of such medical devices include a stent deliverysystem comprising a guidewire, a stent-delivery catheter, a stent, or anembolic protection device.

Still another aspect of the present disclosure is directed to a methodof improving the radiopacity and corrosion resistance of a medicaldevice by making the medical device or a component of it using a binaryalloy of titanium with the other binary element selected from platinum,palladium, or gold.

Various embodiments of the present disclosure can be used in medicaldevices used in arteries, veins, and other body vessels. It is to beunderstood that the present invention is not limited by the embodimentsdescribed herein. Other features and advantages of the present inventionwill become more apparent from the following detailed description of theinvention when taken alone or in conjunction with the accompanyingexemplary drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a stent expanded within the artery, so that the stentmakes intimate contact with the arterial wall.

FIG. 2 depicts a stent according to one embodiment of the presentdisclosure showing the position of radiopaque markers attached thereto.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure is generally directed to titanium containingbinary alloys that can be used in a wide variety of non-medical andmedical applications. While the following discussion exemplifies medicaldevice applications, the disclosure is not so limited. Rather, it isappreciated that the disclosure broadly encompasses any application thatcould utilize the characteristics of radiopacity, weldability, and/orthe high elastic strain limit of the resulting alloy. Therefore, whilethe invention described below is directed to the binary, radiopaquealloy attached to a medical device, or medical devices having componentsmade of such alloys, it is understood that the present invention isapplicable to other medical devices usable in a body lumen or outside abody lumen, or more generally to non-medical devices.

Commercially available materials used in medical devices typicallycomprise superelastic alloys. While such alloys have been extremelysuccessful in applications that exploit their self-expanding properties,such as stents and embolic filtering devices, they typically have poorradiopacity because they comprise low amounts of radiopaque elements.

The present invention improves on existing medical devices by utilizingthe heretofore unappreciated properties of certain binary alloys oftitanium and an element selected from platinum, palladium, rhodium, andgold as a marker on such devices. For example, medical devices, such asstents having the inventive alloys attached thereto, are sufficientlyradiopaque to be readily visualized under fluoroscopy during a stentplacement procedure, yet are not so radiopaque as to interfere with thevisualization of surrounding body tissue or stent lumen. In addition,since the stent comprises a radiopaque material welded thereto, theinventive stent overcomes the drawbacks associated with traditionalcomposite or plated stents, such as retarded deployment and separationof the radiopaque layer.

The stent of the present invention can have virtually any configurationthat is compatible with the body lumen in which it is implanted.Typically stents are composed of an intricate geometric pattern ofcylindrical rings and connecting links. Non-limiting examples ofintravascular stents can be found in U.S. Pat. No. 5,292,331 (Boneau);U.S. Pat. No. 4,580,568 (Gianturco); U.S. Pat. No. 4,856,516(Hillstead); U.S. Pat. No. 5,092,877 (Pinchuk); and U.S. Pat. No.5,514,154 (Lau et al.), which are incorporated herein by reference intheir entirety.

These elements are commonly referred to as struts. Generally, the strutsare arranged in patterns which are designed to contact the lumen wallsof a vessel and to maintain patency of the vessel thereby. A myriad ofstrut patterns are known in the art for achieving particular designgoals. A few of the more important design characteristics of stents areradial or hoop strength, expansion ratio, coverage area and longitudinalflexibility. One strut pattern may be selected over another in an effortto optimize those parameters that are of importance for a particularapplication.

Regardless of the specific application, with most lesion treatmentprocedures, the treated artery suffers a degree of trauma and in acertain percentage of cases may abruptly collapse or may slowly narrowover a period of time due to neointimal hyperplasia which is referred toas restenosis. To prevent either of these conditions, the treated arteryis often fitted with a prosthetic device, such as the stent 10, shown inFIG. 1 of the present invention.

The stent provides radial support for the treated vessel and therebyprevents collapse of the vessel 24 and further provides scaffolding toprevent plaque prolapse within the lumen. The stent may also be used torepair an arterial dissection, or an intimal flap, both of which arecommonly found in the coronary arteries, peripheral arteries and othervessels. In order to perform its function, the stent must be accuratelyplaced across the lesion site.

Therefore, it is desirable that the stent be sufficiently radiopaque sothat the physician can visually locate the stent under fluoroscopyduring the implantation procedure. However, it is equally important thatthe stent not be too radiopaque. If the stent is overly radiopaque thenthe physician's view of the lumen is compromised. This makes assessmentof subsequent restenosis difficult. In cases where the balloon markersare very close to the stent, the stent can blend in with the overlyradiopaque markers. Without precise visualization of the stent ends,accurate placement of the stent in a lesion, particularly in the case ofan ostial lesion, can be compromised.

In a typical stent placement procedure, a guiding catheter ispercutaneously introduced into the cardiovascular system of a patientthrough the femoral arteries by means of a conventional technique, suchas a Seldinger technique, and advanced within a patient's vascularsystem until the distal end of the guiding catheter is positioned at apoint proximal to the lesion site. A guidewire and the stent-deliverycatheter of the rapid exchange type are introduced through the guidingcatheter with the guidewire sliding within the stent-delivery catheter.The guidewire is first advanced out of the guiding catheter into thearterial vessel and is directed across the arterial lesion. Thestent-delivery catheter is subsequently advanced over the previouslyadvanced guidewire until the stent is properly positioned across thelesion.

Referring again to FIG. 1, once in position, the dilatation balloon 16is inflated to a predetermined size to radially expand the stent 10against the inside of the artery wall and thereby implant the stentwithin the lumen 22 of the artery. The balloon is then deflated to asmall profile so that the stent-delivery catheter may be withdrawn fromthe patient's vasculature and blood flow is resumed through the artery.

Since the stent 10 is formed from an elongated tubular member, the ringsand links of the stent are relatively flat in transverse cross-section,thus after implantation into the artery 24, minimal interference withblood flow occurs.

Eventually the stent becomes covered with endothelial cell growth whichfurther minimizes blood flow interference. As should be appreciated bythose skilled in the art, while the above-described procedure istypical, it is not the only method used in placing stents.

Typically, the stent 10 is laser cut from a solid tube. Thus, the stentdoes not possess discrete individual components. However, for thepurposes of description it is beneficial to refer to the exemplaryembodiment of the stent as being composed of cylindrical rings andconnecting links.

In order to achieve the desirable radiopaque properties, the presentinvention uses binary alloy markers welded onto the medical devices thatassist the physician to visually locate the stent under fluoroscopyduring any invasive procedure.

The Inventors have discovered that binary alloys of titanium aremetallurgically compatible when welded to either binary nitinol or aternary nitinol that contains minor amounts of ternary elements, such asup to 10 atomic percent, including the range of 7-8 atomic percent. Inaddition to the improved weldable properties associated withmetallurgical compatibility, the enhanced radiopaque properties make theinventive alloy ideal as a weldable radiopaque marker for medicaldevices. In addition, the disclosed alloys provides radiopaque materialhaving a high elastic strain limit, such as one that is comparable tothat of linear elastic nitinol.

The compatibility of the titanium based binary alloys described hereinlies in the fact that the binary elements described are directsubstitutes for nickel within the nitinol crystal structure.Furthermore, such replacement can occur at any amount up to completesubstitution. Evidence of this phenomenon is show in the phase diagramsfor some known binary alloys, such as nickel-platinum, nickel-titanium,titanium-platinum, and other binary alloys.

For example, as shown in “Binary Alloy Phase Diagrams”, American Societyfor Metals, 1986, which is incorporated by reference herein, the phasediagram for the binary nickel-platinum alloy reveals that mixtures ofnickel and platinum will combine to form one solid solution uponsolidification, regardless of the composition. This is because nickeland platinum atoms are sufficiently alike, such as in atomic radius andelectronegativity, that there are no mixture ratios that correspond tointermediate compounds or phases.

In contrast, the phase diagram for the binary nickel-titanium alloyreveals a variety of phases and compounds, depending on the particularcomposition. This is because Ni and Ti atoms are not nearly as similaras nickel and platinum in atomic radius and electronegativity. One typeof nitinol is a binary alloy of nickel and titanium which containsapproximately 50% nickel and 50% titanium, and is unusual in that itpossesses a reversible martensitic transformation temperature that isresponsible for shape memory and superelastic behavior. In other words,above the martensitic transformation temperature without external load,binary nitinol exists in the austenitic state. Its overall structure isthe B2 crystal lattice, the so called cesium chloride structure. In thisstructure each Ni atom is positioned such that all of its nearestneighbors are titanium atoms and vice versa.

The relatively simple crystal structure and a large number of slipsystems allow binary nitinol to be easily deformed and ductile.Depending upon the composition of the alloy, from about 45% nickelupward to about 55% nickel, the transformation temperature boundary ofthis phase may be lowered.

Similarly, titanium-platinum binary alloys at near equiatomiccompositions exist in a phase which has lattice structure similar tonitinol at above its martensitic transformation temperature. At roomtemperature, the near equiatomic phase is relatively soft and workable.For instance, Ti50Pt50 has a hardness of about 250 HV and is coldrollable to approximately 50% reduction in thickness without edgecracking. The phase boundary is at about 45 and 56% of titanium,corresponding to compositions varying from Ti45Pt55 to Ti56Pt44.

As previously stated, nickel and platinum atoms are sufficiently alikein atomic radius and electronegativity such that the nickel-platinumalloy comprises a solid solution without intermediate phases orcompounds. Other metals that are able to form solid solution with Niwithout intermediate phases or compounds include palladium, rhodium, andgold. Furthermore, platinum, palladium, rhodium, and gold aresignificantly more radiopaque than nickel and can be used in makingradiopaque alloy markers according to the present invention.

The characteristics of nickel-platinum, nickel-titanium,titanium-platinum binary alloys discussed above indicate that, as longas titanium is approximately 50%, platinum may replace nickel in aternary nickel-titanium-platinum alloy up to full substitution and theresulting lattice structure will maintain the same B2 structure.Furthermore, any such ternary composition, designated as Ti50[Ni, Pt]50,will behave in a ductile manner like the binary Ti50Ni50 and Ti50Pt50phases.

In one embodiment, a binary Ti50Ni50 alloy is autogenously welded to aTi50Pt50 alloy marker. As the molten weld pool conforms to thestoichiometry of Ti50[Ni, Pt]50, the resulting weld is essentially freeof undesirable intermetallic compounds. Thus the welded product retainsgood ductility.

Similarly, the Ti50Pt50 alloy marker can form a weld free ofintermetallic compounds to any ternary titanium-nickel-platinum alloythat has a composition at or near Ti50[Ni, Pt]50. For example, inanother embodiment, the radiopaque marker described herein may be weldedto a ternary titanium nickel alloy comprising from 7-8 atomic % ofplatinum, such as Ti50Ni42.5Pt7.5.

By contrast, if a pure platinum marker is welded to a binarynickel-titanium alloy and both components experienced some degree ofmelting, then the bulk composition of the molten weld pool wouldgenerally not maintain Ti50[Ni, Pt]50 stoichiometry. The solidified weldzone may contain a variety of intermetallic compositions, most of whichdo not have a lattice structure similar to Ni50Ti50 or Ti50Pt50. Such aweld could have poor ductility and may tend to crack.

FIG. 2 illustrates a stent showing the inventive radiopaque markersattached thereto. In this non-limiting embodiment, the inventive alloymay be used as proximal (30) and distal (45) markers that are welded,such as by fusion welding, to both ends of the stent. In addition or inthe alternative, small, teardrop-shaped markers, which have been lasercut from the inventive binary alloy or have been formed by other means,can be welded as stent markers (35, 40) to either end of the stent.

As previously stated, the inventive alloys are metallurgicallycompatible with the underlying nitinol substrate (whether binary orternary), thus allowing the radiopaque markers to be fusion welded inplace. As a result, the weld joint of a medical device made according tothe present invention avoids the brittle intermetallic compounds andsubsequent potential cracking typically associated with thermal ormechanical cycling of traditional markers on medical devices.

One embodiment of the present invention is a radiopaque marker thatcomprises a binary titanium-platinum alloy. The atomic percent oftitanium in the alloy may range from 45 to 56, such as from 49 to 51,with the balance comprising platinum.

In another embodiment, the binary alloy comprises an equiatomic amountof titanium and platinum, e.g., Ti50Pt50. The radiopaque marker isintegrally attached to a superelastic alloy, such as by a weld betweenthe radiopaque marker and a superelastic alloy.

In other embodiments of the present invention, the superelastic alloycomprises a binary nickel-titanium alloy, or a ternary alloy of nickeland titanium, and comprising at least one ternary element chosen fromplatinum, palladium, gold and rhodium.

The superelastic alloy according to other embodiments can comprise aternary alloy of nickel, titanium, and platinum, and may be expandableor self-expandable.

In another embodiment of the present invention, the ternary alloycomprises 49 to 51 atomic percent titanium, 7 to 8 atomic percentplatinum, with the remainder comprising nickel.

The present disclosure is also directed to a medical device thatcomprises a radiopaque marker having a binary titanium-platinum alloy asdescribed above. The medical device may include a stent, a guidewire, oran embolic protection device. The radiopaque marker can be integrallyattached to or welded to the stent, the guidewire, or the embolicprotection device.

One non-limiting embodiment of the present disclosure is directed to astent delivery system comprising an expandable or self-expandingsection, and a radiopaque marker integrally attached to the expandableor self-expanding section. The radiopaque marker comprises thepreviously described binary alloy of titanium, which includes one binaryelement selected from platinum, palladium, rhodium, and gold. Thetitanium may be present in the radiopaque marker in an amount rangingfrom 45 to 56 atomic percent, such as from 49 to 51 atomic percent, oreven about 50 atomic percent, with the balance comprising a binaryelement of platinum, palladium, rhodium, or gold.

In the above mentioned stent delivery system the radiopaque marker canbe integrally attached to the expandable or self-expanding section by aweld. The expandable or self-expanding section may comprise a binarynickel-titanium alloy or a ternary alloy of nickel and titanium. Theternary alloy comprises at least one ternary element chosen fromplatinum, palladium, gold and rhodium.

The above-mentioned stent delivery system may further comprise aguidewire. In one embodiment, the guidewire may also have the radiopaquemarker 50 attached thereto.

The invention further provides a method of fabricating a medical devicecomprising a radiopaque marker. The method comprises welding to anexpandable or self-expanding section, a radiopaque marker comprising abinary alloy of titanium and one binary element selected from platinum,palladium, rhodium, and gold.

As stated, fluoroscopy, utilizing x-rays, is by far the most popularimaging method used to visualize medical devices, such as stents. Thisis the case both during an intervention (delivering a stent) andafterwards in a more diagnostic mode. The present invention stent alsois visible under magnetic resonance imaging (MRI), which workscompletely differently from that of fluoroscopy. Thus, a medical devicecomprising the inventive markers will show up in an MRI image in afundamentally different way than under x-ray, primarily as an imagingartifact associated with the magnetic susceptibility and electricalconductivity of the inventive markers.

Any metal that has a magnetic susceptibility different from that oftissue will generate a susceptibility artifact. The magnitude of theartifact depends on how much the susceptibility differs from that oftissue. These artifacts usually are signal voids or dark spots on theimage. Electrically conductive metals in an MRI scanner can also haveelectrical currents induced in them by the radio frequency pulses. Forstents, this can lead to the stent shielding the lumen from the radiofrequency excitation signal.

The medical devices of the present disclosure may be chosen from astent, a guidewire, or an embolic protection device. The methodcomprises welding an above-mentioned radiopaque marker to an expandableor self-expanding section. The welding may comprise fusion welding. Theexpandable or self-expanding section may comprise a binarynickel-titanium alloy or ternary alloy of nickel and titanium. Theternary alloy comprises at least one ternary element chosen fromplatinum, palladium, gold and rhodium. In one exemplary embodiment, theternary alloy may comprise 49 to 51 atomic percent titanium, 7 to 8atomic percent platinum, the remainder nickel. Other exemplaryembodiments are contemplated wherein the percentages of the alloy mayvary as well as the ternary element.

In addition to making radiopaque markers, the inventive binary alloys,which comprise titanium and another element chosen from palladium,platinum, and gold, can also be used to make medical devices orcomponents thereof. Components made of TiPt, TiPd, and TiAu areparticularly suitable as substitute for linear elastic nitinol.

All three equiatomic alloys Ti50Pt50, Ti50Pd50, and Ti50Au50 are similarto equiatomic nitinol (Ti50Pd50) in that all these alloys possess thesame B2 crystal structure at elevated temperatures and the same B19crystal structure at low temperatures. The former is referred to as theaustenitic phase and the latter the martensitic phase. The temperaturerange over which nitinol will spontaneously transform from phase to theother depends upon the composition, i.e., the precise nickel/titaniumratio, and the process history of the alloy. In binary nitinol alloys,the transformation from a martensitic phase to an austenitic phase canoccur above, below, or at room temperature.

In linear elastic nitinol, the crystal structure is martensitic at roomtemperature. One of the ways to attain this characteristics is to beginwith an annealed alloy that is naturally martensitic at roomtemperature, i.e., its transformation temperature is above roomtemperature, and impart an appropriate amount of cold work to increaseits yield stress as needed. If an alloy is austenitic at roomtemperature, its natural transformation temperature is below roomtemperature. Imparting cold work on this alloy can stress-induce themartensitic structure at room temperature while continued cold work willincrease its yield stress.

The transformation temperature of Ti50Pt50, Ti50Pd50, and Ti50Au50 areall substantially above room temperature, so they are naturallymartensitic at room temperature. These alloys can be subject to suitableamounts of cold work, such as wire drawing, tube drawing, rolling orother means, to increase their yield stress. The resulting alloys mayhave a yield stress in the range of 200,000 psi to 250,000 psi and anelastic strain limit ranging from 1% to 3% [8 to 16 Msi, where 1 Msi=10⁶psi].

As discussed in the previous sections, TiPt, TiPd, and TiAu withapproximately 45-55 atomic percent of Ti and the other binary element asthe balance are expected to have similar properties as nitinol. Further,since platinum, palladium, and gold are noble metals, their alloys withTi are more corrosion resistant than nitinol.

Therefore, TiPt, TiPd, and TiAu can be made to have characteristics thatare highly similar to that of linear elastic nitinol, with the addedbenefits of high radiopacity and high corrosion resistance. This makesTiPt, TiPd, and TiAu particularly attractive alternatives for linearelastic nitinol for the purpose of making medical devices.

In one embodiment of the invention, the medical devices or componentsthereof that can be made with TiPt, TiPd, or TiAu include aself-expanding or self-expandable stent, a filter basket in an embolicprotection device, a distal core of a guidewire, and a shaping ribbon ina guidewire. The resulting products will be readily visible usingfluoroscopy procedures, as well as having a better corrosion resistancethan that of nitinol.

In another embodiment of the invention, a stent delivery system having aguidewire, a stent-delivery catheter, a stent, and optionally an embolicprotection device can have one or more components made of TiPt, TiPd, orTiAu components.

One can readily appreciate that, to improve the radiopacity and/orcorrosion resistance of a medical device, one can have the medicaldevices or components thereof made of one or more of the radiopaquebinary TiPt, TiPd, TiAu,

Other than in the operating example, or where otherwise indicated, allnumbers expressing quantities of ingredients, reaction conditions, andso forth used in the specification and claims are to be understood asbeing modified in all instances by the term “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should be construed in light of the number ofsignificant digits and ordinary rounding approaches.

Further modifications and improvements may additionally be made to thedevice and method disclosed herein without departing from the scope ofthe present invention. Accordingly, it is not intended that theinvention be limited, except as by the appended claims.

What is claimed is:
 1. A medical device, comprising: an implantable bodycomprising a superelastic NiTi alloy; a radiopaque marker, saidradiopaque marker comprising a binary alloy of titanium and one binaryelement selected from platinum, palladium, rhodium, and gold, thetitanium present in an amount ranging from 45 to 55 atomic percent andthe balance of the binary alloy comprising said binary element, whereinthe binary alloy is processed to exhibit a yield stress of about 200 ksito about 250 ksi; and an autogenous weld joining the radiopaque markerand the implantable body together, wherein the implantable body, theradiopaque marker, and the autogenous weld exhibit a crystalline latticethat is substantially the same, allowing Ni of the Ni—Ti alloy and thebinary element of the radiopaque marker to substitute for one another inone or more of the autogenous weld, in the implantable body adjacent tothe autogenous weld, and in the radiopaque marker, and wherein theimplantable body, the radiopaque marker, and the autogenous weld aresubstantially free of brittle intermetallic compounds such that theNi—Ti superelastic alloy, the radiopaque marker, and the autogenous weldeach maintain similar ductility.
 2. The medical device of claim 1,wherein titanium is present in an amount ranging from 49 to 51 atomicpercent, with the balance comprising said binary element.
 3. The medicaldevice of claim 2, wherein the binary titanium alloy comprisesequiatomic binary alloys chosen from Ti50Pt50, Ti50Pd50, Ti50Rh50, andTi50Au50.
 4. The medical device of claim 1, wherein said superelasticalloy comprises a binary nickel-titanium alloy or a ternary alloy ofnickel and titanium.
 5. The medical device of claim 4, wherein saidternary alloy of nickel and titanium comprises at least one ternaryelement chosen from platinum, palladium, gold and rhodium.
 6. Themedical device of claim 5, wherein the superelastic alloy is a ternaryalloy of nickel, titanium, and platinum.
 7. The medical device of claim6, wherein the ternary alloy comprises 49 to 51 atomic percent titanium,7 to 8 atomic percent platinum, the remainder comprising nickel.
 8. Themedical device of claim 1, wherein said superelastic alloy is expandableor self-expandable.
 9. The medical device of claim 1, wherein theimplantable body is a stent, guidewire, or embolic protection device.10. The medical device of claim 1, wherein the binary alloy is processedto exhibit an elastic strain limit of about 1 percent to about 3percent.
 11. A stent comprising: an expandable or self-expanding NiTialloy stent body; and a radiopaque marker integrally attached to saidexpandable or self-expanding stent body by an autogenous weld, whereinsaid radiopaque marker comprises a binary alloy of titanium and onebinary element selected from platinum, palladium, rhodium, and gold, thetitanium present in an amount ranging from 45 to 55 atomic percent andthe balance of the binary alloy comprising said binary element, whereinthe binary alloy is processed to exhibit a yield stress of about 200 ksito about 250 ksi, wherein the stent body, the radiopaque marker, and theautogenous weld exhibit substantially the same crystalline lattice,allowing Ni of the Ni—Ti alloy and the binary element of the radiopaquemarker to substitute for one another in one or more of the autogenousweld, in the implantable body adjacent to the autogenous weld, and inthe radiopaque marker such that the Ni—Ti superelastic alloy, theradiopaque marker, and the autogenous weld each maintain similarductility, and wherein the implantable body, the radiopaque marker, andthe autogenous weld are substantially free of brittle intermetalliccompounds such that the Ni—Ti superelastic alloy, the radiopaque marker,and the autogenous weld each maintain similar ductility.
 12. The stentof claim 11, wherein titanium is present in an amount ranging from 49 to51 atomic percent, with the balance comprising said binary element. 13.The stent of claim 12, wherein the binary titanium alloy comprisesequiatomic binary alloys chosen from Ti50Pt50, Ti50Pd50, Ti50Rh50, andTi50Au50.
 14. The stent of claim 11, wherein said expandable orself-expanding stent body comprises a binary nickel-titanium alloy or aternary alloy of nickel and titanium.
 15. The stent of claim 14, whereinsaid ternary alloy of nickel and titanium comprises at least one ternaryelement chosen from platinum, palladium, gold and rhodium.
 16. The stentof claim 11, wherein said ternary alloy of nickel and titanium comprisesplatinum.
 17. The stent of claim 16, wherein the ternary alloy comprises49 to 51 atomic percent titanium, 7 to 8 atomic percent platinum, theremainder comprising nickel.
 18. A stent delivery system including thestent of claim 11, and further comprising a guidewire.
 19. The stentdelivery system of claim 18, wherein said guidewire has a radiopaquemarker attached thereto by an autogenous weld.
 20. The stent of claim11, wherein the binary alloy is processed to exhibit an elastic strainlimit of about 1 percent to about 3 percent.
 21. The medical device ofclaim 11, wherein the stent body, the radiopaque marker, and theautogenous weld exhibit a B2 crystalline lattice.
 22. The medical deviceof claim 11, wherein the autogenous weld includes at least a partialintermixture of metals from the implantable body and the radiopaquemarker and wherein the each of the implantable body, the radiopaquemarker, and the autogenous weld exhibit a B2 crystalline lattice.
 23. Amethod of fabricating a medical device comprising a radiopaque marker,said method comprising: autogenously welding to an expandable orself-expanding NiTi alloy section of the medical device, the radiopaquemarker comprising a binary alloy of titanium and one binary elementselected from platinum, palladium, rhodium, and gold, the titaniumpresent in an amount ranging from 45 to 55 atomic percent and thebalance of the binary alloy comprising said binary element, the binaryalloy exhibiting a cold-work induced yield stress of about 200 ksi toabout 250 ksi, wherein each of the expandable or self-expanding sectionof the medical device, the radiopaque marker, and an autogenous weldcoupling the expandable or self-expanding section of the medical deviceto the radiopaque marker exhibit a metallurgically compatiblecrystalline lattice, allowing Ni of the Ni—Ti alloy and the binaryelement of the radiopaque marker to substitute for one another in one ormore of the autogenous weld, in the implantable body adjacent to theautogenous weld, and in the radiopaque marker, and wherein each of theexpandable or self-expanding section of the medical device, theradiopaque marker, and an autogenous weld are substantially free ofbrittle intermetallic compounds such that the Ni—Ti superelastic alloy,the radiopaque marker, and the autogenous weld each maintain similarductility.
 24. The method of claim 23, wherein titanium is present in anamount ranging from 49 to 51 atomic percent, with the balance comprisingsaid binary element.
 25. The method of claim 24, wherein the binarytitanium alloy comprises equiatomic binary alloys chosen from Ti50Pt50,Ti50Pd50, Ti50Rh50, and Ti50Au50.
 26. The method of claim 23, whereinsaid autogenously welding comprises fusion welding.
 27. The method ofclaim 23, wherein said expandable or self-expanding section comprises abinary of nickel-titanium or a ternary alloy of nickel and titanium. 28.The method of claim 27, wherein said ternary alloy of nickel andtitanium comprises at least one ternary element chosen from platinum,palladium, gold and rhodium.
 29. The method of claim 28, wherein saidternary alloy of nickel and titanium comprises platinum.
 30. The methodof claim 29, wherein the ternary alloy comprises 49 to 51 atomic percenttitanium, 7 to 8 atomic percent platinum, the remainder comprisingnickel.
 31. The method of claim 23, wherein said medical device ischosen from a stent, guidewire, or embolic protection device.
 32. Themedical device of claim 1, wherein the crystalline lattice is a B2crystalline lattice.
 33. The method of claim 23, wherein themetallurgically compatible crystalline lattice includes a B2 crystallinelattice.